Conventionally, a refrigerant cycle device including an ejector is configured to be switched between a cooling operation mode for cooling a space to be air-conditioned, and a heating operation mode for heating the space to be air-conditioned.
In the refrigerant cycle device including the ejector, a refrigerant flow passage is switched so that the cooling operation mode and the heating operation mode are switched. A using-side heat exchanger in which refrigerant is heat-exchanged with air to be blown into the space to be air-conditioned is operated as an evaporator for evaporating the refrigerant in the cooling operation mode, and the using-side heat exchanger is operated as a refrigerant radiator for radiating heat from the refrigerant in the heating operation mode.
FIG. 3 shows a refrigerant cycle device 100A with an ejector 118, described in JP-A-2007-003171 (corresponding to US 2006/0266072 A1), for example. The refrigerant cycle device 100A is provided with a four-way valve 112 as a passage switching portion. The four-way valve 112 is switched such that refrigerant discharged from the compressor 111 is introduced into an exterior heat exchanger 113 to perform heat exchange with outside air while refrigerant flowing out of a diffuser portion 118d of an ejector 118 is drawn to the compressor 111 in the cooling operation mode. In the cooling operation mode, the refrigerant flows as in the solid arrows in FIG. 3. Therefore, in the cooling operation mode, the refrigerant flowing out of the exterior heat exchanger 113 is branched upstream of a nozzle portion 118a of the ejector 118. A part of refrigerant branched from the branch portion flows into a using-side heat exchanger 114 after passing through a decompression unit 119, and is drawn into a suction port 118b of the ejector 118 by a refrigerant stream jetted from the nozzle portion 118a. The refrigerant jetted from the nozzle portion 118a and the refrigerant drawn from the suction portion 118b are mixed in a mixing portion 118c of the ejector 118, and the mixed refrigerant flows through the diffuser portion 118d of the ejector 118. Therefore, in the cooling operation mode, the using-side heat exchanger 114 is operated as an evaporator.
In contrast, in the heating operation mode, the four-way valve 112 is switched so that the refrigerant flows in the chain arrows in FIG. 3. Therefore, in the heating operation mode, the refrigerant discharged from the compressor 111 is introduced into the ejector 118 from an outlet side of the diffuser portion 118d of the ejector 118, and refrigerant flowing out of the exterior heat exchanger 113 is drawn to the compressor 111. In the heating operation mode, the using-side heat exchanger 114 is operated as a refrigerant radiator.
However, in the refrigerant cycle device 100A of FIG. 3, during the heating operation mode, the refrigerant flows in the ejector 118 conversely as compared with the cooling operation mode, and it is impossible to have a pressure increasing efficiency in the ejector 118. As a result, in the heating operation mode, the coefficient of performance (COP) cannot be improved by using the ejector 118.
In a refrigerant cycle device 100B with an ejector 118 described in JP-A-2002-327967 (corresponding to U.S. Pat. No. 6,550,265), two four-way valves 112a, 112b are provided as a passage switching portion, as shown in FIG. 4. In FIG. 4, the components similar to those of the refrigerant cycle device 100A of FIG. 3 are indicated by the same reference numbers. The four-way valves 112a, 112b are switched to perform the cooling operation mode or the heating operation mode. In the cooling operation mode, the refrigerant discharged from the compressor 111 flows into the exterior heat exchanger 113, and the refrigerant flowing out of the using-side heat exchanger 114 is drawn into the refrigerant suction port 118b, as in the solid arrows in FIG. 4. Therefore, in the cooling operation mode, the using-side heat exchanger 114 is operated as the evaporator. In FIG. 4, a gas-liquid separator 120 is located at an outlet side of the diffuser portion 118d of the ejector 118.
In contrast, in the heating operation mode, the four-way valves 112a, 112b are switched so that the refrigerant flows in the chain arrows of FIG. 4. Therefore, in the heating operation mode, the refrigerant discharged from the compressor 111 is introduced into the using-side heat exchanger 114 while refrigerant flowing out of the exterior heat exchanger 113 is drawn into the refrigerant suction port 118b of the ejector 118, and thereby the using-side heat exchanger 114 is operated as the refrigerant radiator.
In the refrigerant cycle device 100B of FIG. 4, in both the cooling operation mode and the heating operation mode, high-pressure refrigerant is supplied to the nozzle portion 118a of the ejector 118, and refrigerant flowing out of the heat exchanger operated as the evaporator is drawn into the refrigerant suction port 118b of the ejector 118. In this case, the COP can be improved in both the cooling operation mode and the heating operation mode, because the loss of the kinetic energy of the refrigerant in the nozzle portion 118a can be recovered and the refrigerant pressurized in the diffuser portion 118d is drawn into the compressor 111. However, according to experiments by the inventors of the present application, the space to be air-conditioned cannot be sufficiently cooled in the cooling operation mode although the space to be air-conditioned can be sufficiently heated in the heating operation mode while improving the COP.
The inventors of the present application studied the reasons in detail and found that the cooling operation mode and the heating operation mode have different effects due to the location conditions of the using-side heat exchanger 114 and the exterior heat exchanger 113.
For example, when the refrigerant cycle device 100B is used for a fixed air conditioner for a room, the using-side heat exchanger 114 is generally located at an upper side in the room so that the room can be effectively air-conditioned. Therefore, the using-side heat exchanger 114 is generally located at a position higher than the exterior heat exchanger 113 that is located at exterior. Thus, in the cooling operation mode in which the using-side heat exchanger 114 is operated as the evaporator, it is necessary to move the liquid refrigerant to the using-side heat exchanger 114 located at a position higher than the exterior heat exchanger 113. Furthermore, in the heating operation mode in which the exterior heat exchanger 113 is operated as the evaporator, the ejector 118 is necessary to provide a refrigerant suction effect corresponding to the head difference between the using-side heat exchanger 114 and the exterior heat exchanger 113.
However, in the refrigerant cycle device 100B of FIG. 4, the refrigerant suction capacity of the ejector 118 is approximately equal in both the cooling and heating operation modes, and the liquid refrigerant is supplied to the heat exchanger as the evaporator by only using the suction effect of the ejector 118, thereby causing an insufficient refrigerant suction capacity in the cooling operation mode. As a result, in the cooling operation mode, a sufficient flow amount of the liquid refrigerant cannot be supplied to the using-side heat exchanger 114, and thereby the space to be air-conditioned cannot be sufficiently cooled.
Furthermore, when the refrigerant cycle device 100B is used for a vehicle air conditioner, the compressor 111 and the exterior heat exchanger 113 are located in the engine compartment, while the using-side heat exchanger 114 is located in a passenger compartment.
When the ejector 118 is located in the engine compartment, a refrigerant pipe connecting the ejector 1118 and the using-side heat exchanger 114 becomes longer as compared with a refrigerant pipe connecting the ejector 118 and the exterior heat exchanger 113. As a result, a pressure loss in the refrigerant passage from the gas-liquid separator 120 to the refrigerant suction port 118b via the heat exchanger operated as the evaporator is increased. Thus, the passenger compartment cannot be sufficiently cooled.